1. Field of the Invention
This invention relates to radial pneumatic tires used for vehicles, and more particular to the design of the lower sidewall and bead area of a run-flat tire to improve the process for manufacturing the tire, mounting the tire on a standard rim and the running performance of the tire on a vehicle.
2. Description of the Art
The building of a tire by conventional means includes initially laying green rubber components one at a time around a cylindrical tire building drum to build-up the carcass and bead portions of the tire. The green tire is then removed from the cylindrical drum and expanded into a toroidal shape before the crown belt plies and tread rubber are added to complete the completing of the green tire ready to be cured in a curing mold. The result is that components that end up in the sidewall of the tire have been rotated approximately 90 degrees during transition going from the cylindrical shape to the toroidal shape during the manufacturing process. The rotation of both the sidewall components and the bead area components about the bead core is typical of one of the possible means of making a tire. The bead core is generally of a high torsional rigidity and does not rotate during this process. This rotation process must be carefully controlled. The rotation problems can be more difficult with the addition of sidewall stiffening members when manufacturing run-flat tires. The need exists in the art to improve the ability to rotate the bead area of the green tire when going from the cylindrical shape to the toroidal shape during the tire building process.
Processes for making a green tire are disclosed in U.S. Pat. Nos. 4,007,069; 4,842,682; 5,215,612; and 5,380,384. These processes show variations in how the toroidal shape is obtained from the cylindrical shape and sidewall components are later added to the toroidal shape by an additional tire building step. These processes are used with green tire building step. These processes are used with green tires having a single bead filler.
The cured tire is mounted on a rim of a vehicle by mechanical means so that the tire is sealed against the rim. The rim transfers the weight of the vehicle through the tire to a ground surface. The mounting of the tire can be difficult as the interface pressure between the tire and the rim must be adequate to maintain inflation pressures in the tire and keep the tire seated on the rim. The interface pressure during mounting becomes very critical with run-flat tires as a result of the stiffer sidewalls and the requirement for the run-flat tire to remain on the rim with a loss of inflation pressure. The bead areas including the bead cores and bead fillers along with the tire sidewalls provide resistance for mounting the tire on the rim. Some tires also include additional stiffening plies such as chafers, flippers and the like that influence the mounting of the tire on the rim. Typical stiffening plies are disclosed in U.S. Pat. Nos. 4,790,364 and 5,033,524. These plies further increase the tire""s radial stiffness when mounting the tire on the rim. A need exists in the art to have better compliance or resilience of the bead filler adjacent the bead core so that the tire can be easily mounted, especially when mounting a run-flat tire on a rim.
The shape, dimensions and material properties of components in the lower sidewall and bead of a tire have a direct effect on the ability to mount the tire on a rim. The tire can be designed to have a compliant shape, dimensions and material properties. The material properties of the filler can be made to be different near the bead core than radially outward in the sidewall to facilitate an efficient tire fabrication process and make the tire easy to mount on a rim. The disclosures of U.S. Pat. Nos. 4,046,183; 4,120,338; 4,508,153; and 5,164,029 and Japan Patent No. 5-178037 illustrate the use of bead fillers having two parts; being one part adjacent a bead core and another part extending into the sidewall area. These two-part bead fillers use different size, shape and material properties for each of the two parts. The bead areas of many of these references also include additional reinforced plies placed adjacent to the bead fillers to improve durability and strength of the bead region of the tire. U.S. Pat. No. 3,682,223 discloses softer cushion strips added between a harder wedge shaped apex strip and the radial wire carcass for improving durability of the tire in the bead area. The need remains in the art to simplify the use of two-part bead fillers in the bead area while maintaining their advantages.
The design of the bead area of the tire is known to have a direct effect on the ride comfort and handling performance of a vehicle. Lateral movements of a vehicle are directly influenced by the lateral stiffness of the tire. The tire""s lateral stiffness is greatly influenced by the bead area design. Bending resilience of the lower bead area of the tire with respect to the rim is a major factor in the lateral stiffness of the tire. The radial stiffness of a tire also has a direct affect on the ride comfort of the vehicle.
The tire design must satisfy a large number of different criteria, some of the criteria being known to be conflicting with other criteria, so that designing a tire with due consideration to both manufacturing issues and performance features remains a challenge. This is especially true when a run-flat tire is being designed which can also run with a loss of inflation pressure.
The need exists in the art to build a green tire having a bead area which can easily be rotated about the bead core when manufacturing the tire and not only provides a cured tire which can be easily mounted on a rim to seat on the rim as discussed above, but also has radial and lateral stiffness properties for improved vehicle handling and ride comfort.
Accordingly, one object of this invention is to provide a method for forming a green tire using a tire building drum such that first and second bead fillers can be laid down in a flat configuration on a tire building drum then positioned radially outward of a bead core during a shaping stage.
Another object of the invention is to provide a tire having an annular bead core in combination with bead filers so that the cured tire can be easily mounted on a rim of a vehicle without excessive inflation pressures so that proper contact is made with the rim, while providing a vehicle with good ride comfort and handling performance.
Yet another object of the present invention is to provide a tire having annular bead cores and bead filers, when designed as a run-flat tire, which has a lower sidewall which is resilient and deforms to the shape of a rim flange during loss of inflation pressure.
A further object of the present invention is to simplify the design of a run-flat tire to reduce the number of difference rubber components used in the bead area when manufacturing the run-flat tire.
In one variation, the invention provides a run-flat tire easily mounted on a rim of a vehicle for normal operation of the vehicle. The tire is useful for many vehicles including passenger cars, light trucks, trucks and the like. The tire has a tread portion for contacting a ground surface and a belt package with belt plies interior to the tread for support of the tread. A plurality of carcass layers positioned interior to the belt plies extend between spaced apart annular beads. The tire has a pair of sidewall portions each extending radially inward from shoulders at lateral edges of the belt package to the annular beads. The spaced apart beads have a unique design including bead areas with first and second bead fillers above the bead cores including the second bead filer with a different hardness and having a gum-drop shape which is enclosed by the bead core and the first bead filler. The method of forming an assembled green tire during the tire building process is also unique to this invention.
The radial pneumatic tire of this invention is for mounting on a rim of a vehicle to sustain vehicle loads by contacting a ground surface at a contact patch of the tire. The tire comprises inner sidewall components including an innerliner and at least one carcass layer disposed to the interior of the tire to retain an inflation pressure within the tire when mounted on the rim and to provide a radial carcass structure under tension when the tire is inflated. A pair of spaced apart annular beads is interconnected by the at least one carcass layer, wherein each one of the annular beads has a bead core, first and second bead fillers and rim interface components for sustaining the tire on a rim when mounted thereupon. The bead core has an annular coil of wire filaments forming a polygonal cross-section having a predetermined tensile strength. The annular beads are spaced apart an axial distance corresponding to a width of the rim on which the tire is to be mounted. Outer sidewall components have sidewall rubber portions and at least one outer carcass layer. The at least one outer carcass layer has a lapping arrangement with at least one inner carcass layer; as one or more of the carcass layers wrap around the bead core. The first bead fillers are each disposed radially from a respective bead core to extend radially into a sidewall area of the tire and are bounded on one side by at least one inner carcass layer and at least one outer carcass layer. The second bead filer is in the form of a gum-drop having a radial inner side adjacent to the bead core and bounded by the first bead filler on the other sides of the second bead filler. A crown portion of the tire has a belt package radially outward of the inner sidewall components and a tread for making contact with the ground surface at the contact patch for supporting the vehicle.
The present invention includes a unique method for forming a tire in a tire building process from a green tire using a cylindrical tire building drum. The method comprises the following steps. The first step includes providing inner sidewall components and rim interface components of the green tire including an innerliner and at least one inner carcass layer and placing the inner sidewall components and the rim interface components around an outer surface of tire building drum. The rim interface components including blastomeric rubber portions and turn-up portions of the at least one carcass layer. In a second step the method includes providing a pair of bead cores having an annular coil of wire filaments and placing the bead cores axially spaced apart in a position radially outward of respective rim interface components, and providing a pair of first bead fillers having an axially elongated and tapered cross-sectional shape and placing each one of the first bead filers around the outer surface of the building drum with a short axial outer edge adjacent to an axial inside edges of a respective bead core in a flat position radially to the outside of the inner sidewall components. The third step of the method includes providing a pair of second bead fillers having a gum-drop shape and placing each one of the second bead fillers around a respective bead core so that a radial internal edge of the second bead filler is adjacent to a radial outer edge of the respective bead core. A fourth step includes folding the rim interface components at each lateral edge around a respective bead core and second bead filler to interface with a radial outer face of the first bead filler. A fifth step includes placing outer sidewall components having sidewall rubber components and at least one outer carcass layer around the building drum between the bead cores radially outward of the inner sidewall components and the first bead filler and lapping the at least one inner carcass layer with the at least one outer carcass layer. In a sixth step the method includes shaping said assembled components into a toroidal shape by forcing the pair of bead cores to approach one another while rotating the first bead filler and the rim interface components about each respective bead core and second bead filler.
Additional embodiments of the method for providing a cured tire for use on a vehicle comprise the further steps of: adding a belt portion and a tread rubber to a crown area of the assembled components to provide an assembled greet tire; curing the assembled green tire in a tire mold and providing a cured tire, wherein each second bead filler is positioned to have one side adjacent to the respective bead core, to extend radially outward of the respective bead core and to be bounded on by the first bead filler on the other sides of the second bead filler; and mounting the cured tire on a rim of a vehicle for transferring loads from the vehicle to a ground surface by way of the rim and cured tire for running of the vehicle. Other variations and combinations of steps can be provided, namely according to the manufacturing machines available.